The present invention relates to switching circuits for the electromotor driving fan cooling an engine in a motor vehicle. Specifically, it relates to such circuits wherein a control circuit energizes the electromotor independently of the state of the ignition switch means when the temperature of the engine exceeds a predetermined temperature. The control circuit includes a thermostat which closes when the engine temperature exceeds said predetermined temperature.
In these known arrangements, the electromotor driving the fan can be energized whenever the engine temperature exceeds the predetermined temperature even when the ignition switch is open, since the energization of the electromotor is independent of the ignition switch. Thus the known arrangements effectively combat the condition wherein the motor temperature rises possibly over 120.degree.C. after the engine has been shut off. This rise in temperature often resulted in as bubbles in the gas feed line which made the next starting operation of the motor extremely difficult. Further, the increase in temperature following the engine shut off used to result in steam bubbles in the cooling system and damage to other temperature sensitive elements within the engine, such as, for example, a bearing damage.
The known circuits prevent all the above damage since the fan continues to blow after the engine switch has been turned off. However, since the electromotor driving the fan is energized independently of the ignition circuit, these known systems allow the fan to be activated whenever ambient conditions such as, for example, strong sunlight, cause the motor temperature to rise above a predetermined temperature. Thus if the automobile is parked in a strong sunlight it is possible that the battery is worn out by the excessive use of the fan and that the next starting operation cannot be carried out.